# Cosmic microwave background (CMB) radiation is detected uniformly across the entire sky. Explain what CMB radiation is and why its existence supports the Big Bang theory.

> WJEC GCSE Physics (Wales) — 2.6 Particle physics and using physics to investigate the universe · Explain · 4 marks

> Astronomers can detect a faint microwave radiation coming from all directions in space. This radiation was first detected accidentally in 1965 and has since been studied in great detail.

## Mark scheme (4 marks)

1. CMB radiation is electromagnetic/microwave radiation that fills the entire universe
2. CMB radiation is the remnant/leftover energy/radiation from the Big Bang itself
3. The Big Bang theory states the universe began extremely hot and dense, and this early radiation has been cooling/stretching as the universe expanded
4. The fact that CMB radiation is detected uniformly in all directions supports the idea that the Big Bang occurred everywhere at once / the universe expanded from a single point

## Key terms

- [Big Bang](https://www.gradenine.co.uk/glossary/big-bang)

## Related

- [Revision notes for WJEC GCSE Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/cosmic-microwave-background-cmb-radiation-is-5c79e7e7) · Published by Druglandscape Ltd.